The present exemplary embodiment relates to metal doors. It finds particular application in conjunction with metal doors and methods for making the same that wherein a pan is joined with a lid, and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiment is also amenable to other like applications.
Commercial doors and frames of various styles have been widely available for many years. Such doors and frames generally include wood doors and frames, hollow metal doors and frames, and a wide variety hardware. The term “hollow metal” describes door and frame assemblies manufactured by forming sheet metal, normally in ranges from 20-14 gauge in doors and 18-12 gauge in frames. The end products are essentially hollow (versus their more-solid wood counterparts), hence the term. Hollow metal door designs generally follow one of two patterns for constructing the assembly shell—the perimeter-channel design and the pan-and-lid design.
Doors constructed according to the perimeter-channel design include front and back panels joined together in a seam along the center of the vertical door edges (e.g., hinge edge and lock edge). This design generally incorporates a perimeter framing of channels that are welded to the adjoining faces of the door assembly through weld projections in the channel components. The door assembly is strengthened by the frequent welds along the full perimeter of the door faces but at the cost to aesthetics with the visible exterior imperfections from the welding of projections through the interiors of panel faces. Besides the aesthetical objection of the weld marks, a significant manufacturing drawback of the perimeter-channel design is the absence of a “carrier” sub-assembly to facilitate progressive assembly. Tasks cannot easily be spread evenly to maintain a balanced flow. Bottlenecks frequently occur at the assembly step where an unbalanced amount of work converges. Accordingly, producing doors of the perimeter-channel design is more difficult.
The pan-and-lid design includes front and back panels that necessarily differ in size because they join together in a seam offset to a common side of the vertical door edges. This offsetting creates a “pan” with side edges that approach the full thickness of the finished assembly. The mating “lid” is relatively flat and configured to mate with the side edges of the pan.
Existing pan-and-lid door designs incorporate various mechanical engagements along the vertical edges of the door height. These mechanical methods include folding/seaming of panel edges or interlocking of tabs and slots in conjunction with adhesives. These methods have existed for several years.
One of the most beneficial features of the pan-and-lid design is that the pan sub-assembly provides a convenient “carrier” through the assembly processes. To this carrier, internal components can be attached or assembled with relatively open access in steps that can be separated and balanced into an even flow for productivity. Another significant benefit is the reduction in material costs through elimination of hinge and lock channels.
A critical element of the pan-and-lid designs is their dependency on adhesive to bond, strengthen and secure the mechanical interlocking. Inadequate or improper application of the adhesive compromises the assembly strength as the mechanical engagement could otherwise disengage. Immediately following assembly, the door is susceptible to twisting or racking from handling until the adhesive is set. In use, the adhesive is subject to fracture and failure from impacts such as uneven closing contact.
Accordingly, while pan-and-lid design doors are more easily mass-produced, they have heretofore suffered from the aforementioned shortcomings